Systems managing presence or absence of a managed object by using an ultra-high frequency (UHF) band passive radio frequency identification (RFID) system becoming widespread in recent years have been proposed. For example, WO 2014/041715 being PTL 1 describes a method of placing an RFID tag in a managed object placement area instead of affixing an RFID tag to a managed object, and detecting presence or absence of the managed object in the managed object placement area, based on a strength or a phase of a reflected signal from the RFID tag, the strength or the phase being changed depending on a change in an antenna operating characteristic of the RFID tag based on presence or absence of the managed object.
On the other hand, technologies related to an RFID system performing inventory management by affixing an RFID tag to a managed object are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2011-114633 being PTL 2, “ANTENNA DEVICE, AND SYSTEM INCLUDING ANTENNA DEVICE,” Japanese Unexamined Patent Application Publication No. 2012-117905 being PTL 3, “RFID TAG POSITION DETECTION DEVICE AND RFID TAG POSITION DETECTION METHOD,” and Japanese Unexamined Patent Application Publication No. 2006-197202 being PTL 4, “INFORMATION SYSTEM USING ELECTRONIC TAG AND ELECTRONIC TAG.”
The technologies disclosed in aforementioned PTLs 2 to 4 affix an RFID tag to a managed object, and when tag information of the RFID tag receiving a signal radiated from an RFID reader antenna can be read, determine that the managed object corresponding to the tag information exists within a range in which tag information of the RFID tag can be read from the RFID reader antenna. On the other hand, when tag information of the RFID tag cannot be read, the technologies determine that the managed object corresponding to the tag information does not exist within the range in which tag information of the RFID tag can be read from the RFID reader antenna. Thus, the technologies disclosed in aforementioned PTLs 2 to 4 manage presence or absence of a managed object while identifying the managed object by reading tag information affixed to the managed object.